Dental prosthesis and method of manufacture



April 25, 1961 R. L. COLEMAN ET AL 2,980,998

DENTAL PROSTHESIS AND METHOD OF MANUFACTURE Filed Feb. 4, 1957 GOLD ALLOY CAST/N6 POPCELA/A/ VENEER FIG.'Z

INVENTORS R/CHAPD L. COLEMAN PAUL s. CEC/L BY dUL/U A KEPPEL AT ORNEYS alloys having United States Patent DENTAL PROSTHESIS AND METHOD OF MANUFACTURE Richard L. Coleman, West Hartford, Conn., Paul S. Cecil, Newark, N.J., and Julius A. Kerpel, Flushing, N.Y., assignors to The J. M. Ney Company, Hartford, Conn., a corporation of Connecticut Filed Feb. 4, 1957, Ser. No. 638,121

s Claims. 0132-12 The present invention relates to the field of dental prosthetics and more particularly to a new and improved dental phosphetic device or restoration which is formed by the direct bonding of a new and improved porcelain to a novel casting gold alloy.

The advantages and desirability of using porcelain as a tooth-colored material in dental prosthetics have long been recognized and it also is well-known that a casting gold alloy, in general, is superior in most respects for use as a crown and bridge material. However, prior to the present invention, it has not been possible to combine these materials in the production of a satisfactory dental prosthetic device or restoration meeting the strength and aesthetic requirements of modern practice and utilizing ordinary dental oflice or laboratory equipment and techniques.

One expedient practiced heretofore has been to form a gold alloy casting and a porcelain facing as separate structures, then to join the two with a third or cementing material and with or without a mechanical interlock. Such dental restorations are generally disadvantageous because of the weakness and difficulty of forming the bond as well as the likelihood of seepage of mouth fluids into the interface creating discoloration and disagreeable odors.

Attempts have been made to find possible acceptable substitutes for casting gold alloy or porcelain or both which can be directly bonded to each other but without success or consistent results. For example, platinumiridium or other high fusing noble metal alloys have been tried but found to be too diflicult to cast with consistent accuracy in the average dental oflice or laboratory and the porcelain has a tendency to develop cracks during or after firing. Even if they could be used successfully, such metals would lack the aesthetic advantage of the color of gold. Wrought metals have been tried and discarded because of theextreme difiiculty of forming a complicated dental structure by merely shaping and bending wrought metal stock. Plastics in place of porcelain have been proposed, but color control is difficult and behavior in the mouth has not been ideal.

It has been proposed heretofore to form dental restorations by fusing porcelain directly to gold alloy but such attempts to form acceptable dental restorations have been unsuccessful. A principal difiiculty has been the inherent tendency of porcelains heretofore known to become discolored when fired in contact with available gold suitable hardness and strength characteristics for this purpose. Various techniques have been attempted for oxidizing and pickling the surface of gold alloy castings to overcome the discoloration effect but such techniques are not only unduly complicated but in addition are so inconsistent that the production of natural shades has been found to be virtually impossible.

Inaccordance with the present invention, a new gold alloy and a new porcelain have been provided which are synergetic and mutually cooperative to permit the fabrication of a dental prosthetic device or restoration comprising a gold alloy casting of preferred hardness and strength characteristics and a porcelain facing directly fired and bonded thereon, free from tendency to separate or chip, utilizing ordinary dental office or laboratory equipment and techniques and affording good and consistent results from the standpoint of accuracy, aesthetic appeal and color, and behavior in the mouth.

The gold alloy of the present invention is composed of gold to which is added small amounts of platinum and/or palladium, copper, anda deoxidizing metal such as zinc, indium and/ or tin. It has been found that the desired properties of a gold alloy for use in the present invention, namely, an ability to form a strong bond directly to the porcelain of the present invention without discoloration or cracking of the porcelain, a sufliciently low melting range to permit melting and casting with the usual dental office equipment but high enough to permit the firing of the porcelain, and a gold color, can be obtained by forming the alloy of the components men- The proportion of the above alloying elements may be varied within the limits specified depending upon the particular type of application or restoration contemplated. It will be realized that in some dental prostheses or restorations such as long-span bridges, greater strength is required than in other examples such as veneer crowns for a single tooth. It also will be realized that for some uses lower or higher melting ranges will be desirable. In general, decreases in the platinum and/ or palladium content and increases in the amount of low-fusing deoxidizing metal present will lower the melting point. In combination with the porcelain of the present invention, increases in the amount of copper present within limits will increase the strength of the bond as well as increase the hardness and decrease the melting point of the casting. However, an excessive amount of copper will cause discoloration of the porcelain.

It will be realized that small amounts of other metals, particularly as impurities, may be present without departing from the essential characteristics of the alloy. However, it should be pointed out that the proportion of the alloying elements are critical for the purposes and aims of the present invention and the addition of other metals should be avoided in the absence of careful investigation of possible adverse efiect. For example, even as little as three parts of silver, a common alloying metal frequently used for economy reasons in dental work, when present in the alloy of the present invention, will cause noticeable discoloration of the porcelain.

The porcelain of the present invention can be fired directly on the gold alloy described above and provides good adherence without undue discoloring and without forming cracks. In addition, it has a high breaking strength and is inert to mouth fluids maintaining a desirable lustre or finish indefinitely and it accepts mineral coloring oxides readily so that human tooth colors may be efiectively duplicated. In the preferred embodiment of the invention, the porcelain is preferably applied to the gold alloy casting in two or more layers, the first layer being relatively opaque to block out the shadow of the casting and the second or additional layers being relatively translucent.

The opaque porcelain composition of the present invention in powder form is formed by fritting and milling together the following ingredients within the ranges specified:

Opaque porcelain (powder) Maximum Optimum Range, Range,

parts parts Feldspar 3 to 9 5 to 7 Clay 4 to 10 6 to 8 t0 2 0 to .5 35 to 55 40 to 50 8 to 16 9 to 12 Flurospar 0 to 1 .1 to .2 Borax 15 to 25 17 to 20 Sodium nitrate 0 to 4 1 to 2 Soda ash 3 to 9 5 to 7 Calcium carbonate.. .5 to 3 .5 to 1. 5 Barium carbonate 0 to .5 0 to .2 Phosphorous pentoxide .1 to 1. 5 .2 to 1. 5 Potassium silieofluoride 1 to 6 2 to 4 After fritting and milling, the optimum composition by weight of the powder is as follows:

Parts K 0 2.0-3.5 Na O 7.0-9.0 CaO 0.2-1.0 BaO 0.0-0.2 A1 0 3.0-5.0 i 8 32f? Si O IIIT 'TIIIIII 60.0-67:O TiO 9.0-12.0 Fq 0.0-2.5

The translucent porcelain of the present invention in powder form is made by fritting and milling together the following ingredients within the ranges specified.

Translucent porcelain (powder) After fritting and milling, the optimum composition by weight of the powder is as follows:

Parts K 0 1.5 to 2.5 Na O 6.0 to 8.0 CaO 0.5 to 1.5 BaO 0.1 to 0.2 A1 0 2.0 to 3.0 B203 3.0 to 4.5 SiO 72.0 to 80.0 TiO 4.0 to 6.0 F; 0.0 to 0.2

As will be realized, the porcelain powders just described above are formed into a fluid paste or creamy mixture by the addition of water and this paste or creamy liquid is utilized in shaping the artificial tooth structure which is thereafter cured by the firing operation. Usually, only a very small quantity of the opaque porcelain is utilized since the object is to merely cover the gold casting without reducing the thickness of the translucent portion any more than is necessary. Usually a layer of as little as of an inch is suflicient for shadow blocking purposes. The preferred practice is to fire the opaque layer before the application. of the translucent layer.

The carrying out or use of the invention is illustrated in the, accompanying drawings in which- Fig. 1 is a perspective view of a casting for a central veneer crown formed of the gold alloy of the present invention; and

Fig. 2 is a perspective view of the completed restoration with the veneer crown of porcelain of the present invention directly fired on the casting.

In accordance with the invention the first step in producing a dental prosthetic device or restoration is to form the gold casting using the gold alloy of the present invention and utilizing conventional dental laboratory and dental ofiice techniques. After the casting is formed it is preferred to completely polish all surfaces which are exposed in the final prosthetic device or restoration while the portions to which the porcelain is to be applied are left with a stone or burr finish. After polishing, the cast ing is thoroughly cleaned of all polishing materials by boiling in a detergent solution. When feasible, a try-in of the casting should be made in the mouth before the porcelain is fired to it, since adjustments in form, occlusion and contact points are preferably made before the porcelain is added.

In the application and firing of the porcelain, conventional dental techniques are employed. A thin layer of opaque porcelain is first applied as mentioned above in the form of a creamy mixutre. This can be done conveniently with a brush since only a very thin coating of the order of about ,4 of an inch is sufficient. Any of the porcelain which is carried over the margins of the veneer area should be removed before firing. After the opaque layer is applied, it is permitted to dry preferably in the presence of warm air and then the casting with applied opaque layer is placed in an oven which is at a temperature at or slightly below 1100 F. The temperature is then raised gradually until a temperature of approximately 1550 F. is reached whereupon the assembly is removed and permitted to cool slowly such as by placing it under a glass tumbler or beaker. It is preferred not to apply heat higher than 1550 F. at this stage inasmuch as the opaque layer will have to stand at least one or more additional firings when the remainder of the porcelain is applied. As with all other dental porcelains, the degree of maturing depends not only on the final temperature but also on the rate of heating and the time the final temperature is held. If fired at a faster rate, the porcelain would require a higher temperature or a longer holding time. If fired at a slower rate a lower temperature or shorter holding time is required.

After the opaque layer has been applied and fired, the body porcelain is applied over the opaque porcelain layer. The translucent porcelain powder is mixed to a creamy consistency with distilled water after adding the desired mineral coloring oxides to produce the shade desired. The creamy mixture is applied over the opaque layer with a spatula in small increments and each portion is vibrated to bring excess water to the surface where it is removed with a soft cloth. The veneer is built up to the desired thickness and then dried as, for example, before the open door of a furnace. After the crown is dried it is inserted in a preheated furnace at a temperature of approximately 1100 F. The firing rate may be the same as for the opaque layer but the temperature preferably is carried to 1650 F. Again, the assembly is permitted to cool slowly such as by placing it under glass.

After cooling has been completed any necessary discing and shaping is done with sandpaper discs and small stones. Then when all grinding and discing is completed the surface is thoroughly scrubbed in soap and water with a clean, stiff brush. Thereafter, the restoration is dried and some dry translucent porcelain powder is thoroughly rubbed into the surface with the finger to fill up the pores on the surface. Thereafter, it is again preheated and given a final firing to produce the desired glaze. After cooling, the restoration is placed in a sulphuric acid bath and heated to remove all oxidation from the gold following which the gold is repolished.

By following the foregoing technique with the gold alloy and porcelain of the present invention there will be formed a strong adherence between the porcelain and the gold alloy and the porcelain will be free from cracks and will be relatively inert to mouth fluids. While it is not intended to limit the invention to any particular theory of operation, nonetheless, it is believed that the unusual adherence between the gold alloy and the porcelain is probably due to the ability of the porcelain to wet the surface of the gold alloy suflicientily well enough so that oxides formed during firing are dissolved in the liquid at the interface. It also is believed that the freedom from cracking of the porcelain is probably due to the coefi'icient of expansion of the porcelain in relation to the metal. Since the opaque porcelain layer has a lower coeflicient of expansion than the gold alloy, and the translucent porcelain has a lower coefficient than the opaque layer,

the result is that the porcelain is placed under compres- Percent Gold 81 Platinum g Copper 8 Zinc 1 This specific gold alloy has a melting range of approximately 1880 to 1930 F. which, of course, is within the range permitting melting and casting with the usual laboratory equipment and accessory materials. The tensile strength of this particular gold alloy is 60,000 pounds per square inch and the Brinell hardness is 100. Thus, it will be seen that the alloy has requisite characteristics for use even in long-span bridges and this strength is not reduced by repeated firings of the porcelain. In the event that it is necessary or desirable to form a bridge framework by assembling a number of cast units, a gold alloy of the present invention having a lower melting range may be utilized as a solder. A specific example of a gold alloy of the composition of the present invention and having a lower melting range of the order of 1800 to 1830 F. is as follows:

- Percent Gold 85 Palladium I 5 Copper 6 Zinc 4 A specific example of an opaque porcelain powder coming within the scope of the present invention is one formed by fritting and milling together the following mixture:

A specific example of the body or translucent porcelain is one formed by fritting and milling together the following ingredients:

The foregoing specific examples of gold alloy and porcelains have been made into various types of restorations such as veneer crowns, Richmond type crowns, bridges, etc. In each case, a casting was first made with the gold alloy and then the porcelain was fired thereon in accordance with the technique described above. In all cases there was no discoloration or cracking of the porcelain and a strong bond was formed between the gold alloy and the porcelain. Accelerated corrosion tests, plus use in the mouth, have shown conclusively that these materials are unaffected by mouth fluids and maintain their lustre and finish indefinitely. No failure of the casting or porcelain or bond therebetween has been encountered.

To illustrate the strength of the bond between the gold alloy and the porcelain, pairs of cast rods of the gold alloy of the first specific example were joined together with the porcelains also given by way of specific example and fired as described above. These rods joined together by the porcelain were then held in the clamps of a tensile testing machine and pulled apart. Invariably, the break occurred through the porcelain instead of the porcelain pulling away from the gold, demonstrating that the strength of the bond is greater than that of the porcelain. This is entirely unexpected particularly because the porcelain itself has a higher breaking strength than that of other dental porcelains commercially available. I A porcelain rod approximately A" square by 1" long formed of the translucent porcelain of the specific example given above and subjected to a modulus of rupture test showed a breaking strength in pounds per square inch of over 9,000.

It thus will be seen from the foregoing description that a new and useful dental prosthetic device has been provided combining the features of a new and improved gold alloy with a new and improved porcelain composition. It is contemplated that some variations will be apparent to one skilled in the art and all such variations are intended to be included within the scope of the invention.

We claim:

1. A dental prosthetic device comprising a casting of a gold alloy consisting essentially of to parts gold, 3 to 12 parts of one or more metals selected from the group consisting of platinum and palladium, 5 to 10 parts copper, and 0.5 to 4 parts of one or more deoxidizing metals selected from the group consisting of zinc, indium and tin, and a porcelain facing fired on and directly bonded to a surface of the casting comprising a first layer consisting essentially of the following composition:

Parts by weight K20 2.0-3.5 E t" 32*?8 a BaO 0.0-o.2 A1203 3.0-5.0 as an 2 5 sio 60.0-67.0

Parts by weight TiO 9.0-12.0 F 0.0-25

and a second layer consisting essentially of the following composition:

Parts by weight K 1.5-2.5 Na o 6.0-8.0 CaO 0.5-1.5 BaO 0.1-0.2 A1203 2.03-0 B O 3.0-4.5 $1 0 72.0-80.0 Tio 4.0-6.0 F 0.00.2

2. An opaque porcelain for use in dental prosthetics consisting essentially of the following composition:

Parts by weight 3. A translucent porcelain for use in dental prosthetics consisting essentially of the following composition:

Parts by weight K20 1.5-2.s Na 0 6.0-8.0 CaO 0.5-1.5 BaO 0.1-0.2 A203 2.0-3.0 B203 3.0-4.5 sio 72.0-80.0 "rio 4.0-6.0 F2 0.0-0 2 4. A method of forming a dental prosthetic device comprising forming a casting of a gold alloy consisting essentially of 70 to 90 parts gold, 3 to 12 parts of one or more metals selected from the group consisting of platinum and palladium, to parts copper, and 0.5 to 4 parts of one or more deoxidizing materials selected from the group consisting of zinc, indium and tin; forming a thin coating of opaque porcelain bonded directly to the casting by firing at elevated temperature a thin layer consisting essentially of the following composition:

Parts by weight K20 2.0-3.5 Na O 7.0-9.0 CaO 0.2-1.0

BaO 0.0-0.2 A1203 3.0-5.0 5 8 3'31? 2 5 sio 60.0-67.0 rio 9.0-12.0 F 0.0-2.s

and thereafter forming a second coating of translucent porcelain over the first coating of opaque porcelain by firing at elevated temperature a layer consisting essentially of'the following composition:

Parts by weight K 0 1.5-2.5 Na O 6.0-8.0 CaO 0.5-1.5 BaO 0.1-0.2 A1 0 2.0-3.0 B 0 3.0-4.5 SiO 72.0-80.0 TiO 4.0-6.0 F 0.0-0.2

5. A method of forming a dental prosthetic device comprising forming a casting of a gold alloy consisting essentially of to parts gold, 3 to 12 parts of one or more metals selected from the group consisting of platinum and palladium, 5 to 10 parts copper, and 0.5 to 4 parts of one or more deoxidizing metals selected from the group consisting of zinc, indium and tin; applying to a surface of the casting a thin layer consisting essentially of the following composition:

Parts by weight K20 2.0-3.5 Na O 7.0-9.0 CaO 0.2-1.0

BaO 0.0-0.2 A1203 3.0-5.0 2e

2 5 --1-5 510 60.0-67.0 Tio 9.0- 2 0.0-2.s

firing the coated casting at a temperature not exceeding approximately 1550 F., thereafter applying a second coating layer consisting essentially of the following composition:

Parts by weight and thereafter firing the coated casting at a temperature not exceeding approximately 1650 F.

References Cited in the file of this patent UNITED STATES PATENTS 1,615,247 Taylor Jan. 25, 1927 2,050,040 Coleman et al. Aug. 4, 1936 2,077,481 Huppert Apr. 20, 1937 2,118,934 Madzar May 31, 1938 2,194,790 Gluck Mar. 26, 1940 

1. A DENTAL PROSTHETIC DEVICE COMPRISING A CASTING OF A GOLD ALLOY CONSISTING ESSENTIALLY OF 70 TO 90 PARTS GOLD, 3 TO 12 PARTS OF ONE OR MORE METALS SELECTED FROM THE GROUP CONSISTING OF PLATINUM AND PALLADIUM, 5 TO 10 PARTS COPPER, AND 0.5 TO 4 PARTS OF ONE OR MORE DEOXIDIZING METALS SELECTED FROM THE GROUP CONSISTING OF ZINC, INDIUM AND TIN, AND A PORCELAIN FACING FIRED ON AND DIRECTLY BONDED TO A SURFACE OF THE CASTING COMPRISING A FIRST LAYER CONSISTING ESSENTIALLY OF THE FOLLOWING COMPOSITION: AND A SECOND LAYER CONSISTING ESSENTIALLY OF THE FOLLOWING COMPOSITION: 